(a) Field of the Invention
The present invention relates to a sample centering system, and more specifically to a sample centering system for quantitative analyses of fractionated patterns of sera by the electrophoresis.
(b) Description of the Prior Art
In the electrophoresis, samples such as sera are applied onto a carrier made of cellulose acetate or the similar material, the carrier is electrically energized to form fractionated patterns of the samples, the carrier is colored, discolored and made transparent, and then the samples are colorimetrically measured for quantitative determinations. In order to automatically perform the state of colorimetry for quantitative determinations out of these steps for the electrophoresis, the carrier is shifted between a light source and a photo detector, stopped each time a sample is located just between the light source and photo detector, and the sample is scanned for colorimetry by shifting the light source and photo detector as a combination, for example, in the direction perpendicular to the shifting direction of the carrier. For this purpose, it is necessary to detect positions of the samples applied onto the carrier and stopping it each time a sample is located just between the light source and photo detector.
Construction of an example of the conventionally known sample detectors is illustrated in FIG. 1, in which the reference numeral 1 represents a carrier, the reference numeral 2 designates samples applied onto the carrier at definite intervals, the reference numeral 3 denotes a light source assembly for photometry consisting of a light source lamp 4, a lens system 5, a filter 6, a slit 7, etc., the reference numeral 8 represents a photo detector for photometry consisting of a slit 9 and photo detector elements 10, the reference numeral 11 designates a plural number of optical fibers having ends 11a which are arranged under the passage of the carrier in the direction perpendicular to the shifting direction of the carrier as shown in FIG. 2, the reference numeral 12 denotes a light source lamp arranged in the vicinity of the other ends 11b of the optical fibers 11, and the reference numeral 13 represents plural number of photo detector elements which are arranged over the passage of the carrier so as to receive light emerging from the optical fibers. A sample detector system is composed of these optical fibers, photo detector elements and so on. When the carrier 1 is shifted by an adequate shifting means in the direction indicated by arrow A as shown in FIG. 1 in the sample detector having the above-described construction, the rays emerging from the individual optical fibers 11 pass through the carrier 1 and are received by the individual photo detector elements 13. The photo detector elements 13 provide high outputs while transparent portion 1a of the carrier 1 is positioned between the ends 11a of the optical fibers 11 of the sample detector system and the photo detector elements 13, whereas the photo detector elements 13 provide low outputs when the sample 2 applied onto the carrier 1 is located between the ends 11a of the optical fibers 11 and the photo detector elements 13. It is therefore possible to detect position of the sample 2 on the basis of the outputs from the photo detector elements 13. After the position of the sample is detected with the sample detector system, the optical axis of the photometric system consisting of the light source assembly for photometry and the photo detector system for photometry can be aligned with the center of the sample by stopping the carrier 1 after further shifting the carrier 1 for a definite distance determined by the distance as measured from the sample detector system to the photometric system and so on.
Detection of the sample position with the above-described sample detector system will be described with reference to FIG. 3 and FIG. 4. The outputs from the photo detector elements 13 are amplified by an amplifier 14, whose output a is compared, in a comparator detector circuit 16 in a sample detector circuit 15, with a signal a' provided by a threshold level signal generator 17. The signal a' provided by the threshold level signal generator 17 is a signal kept at a preset constant level as shown in FIG. 4. When the comparison between the output a and signal a' indicates coincidence of both the signals, a sample detection signal b is generated. This sample detection signal b functions to turn on a shifting timer 18, which in turn generates a signal c. Since this signal c is turned off in a certain definite time, a carrier shifting signal d already provided from a controller 19 is turned off at the falling time of the signal c. Therefore, a carrier shifting mechanism 20 which is driven by the carrier shifting signal d from the controller 19 is stopped when the signal d is turned off to stop the carrier. When the shifting timer is set for a time interval just for shifting the carrier for a distance 1 shown in FIG. 1, the carrier is stopped the moment that the center of the sample 2 is aligned with the optical axis of the photometric system. In other words, for the above-described example which detects the rear end of the sample with the sample detector system, the shifting distance after detection of the sample to stopping of the carrier is equal to the distance between the photometric system and the detector system minus half the length of the sample in the carrier shifting direction (more strictly, the length as measured from the front end of the sample to the point at which signal level corresponding to the rear end of the sample becomes coincident with the threshold level signal).
In the above-described sample detector, however, the comparator detector circuit 16 does not provide the signal b in case of a sample at such a low concentration that the sample detection output signal a.sub.1 is not lowered (darkened) to the threshold level, thereby making it impossible to detect the sample. Further, in case of a sample at such a low concentration that the sample detection output is close to the threshold level, detection is made unstable. On the other hand, in case of a sample at such a high concentration as to provide sample detection signal a.sub.2 shown in FIG. 5, the sample is continuous with the neighboring one due to diffusion, whereby the output corresponding to the section between samples a.sub.2 and a.sub.3 is not higher (brighter) than the threshold level. It is therefore impossible to discriminate the two samples from each other, thereby constituting possibility to judge the two samples as one and proceed to analysis of the next sample without performing photometry of one of the samples a.sub.2 and a.sub.3. As a result, analytical result of the sample which is not subjected to photometry is not recorded and skipped on a clinical card in transferring clinical data, etc. If such skipping is not noticed in transferring analytical data, correspondence between samples and patients will be erroneous on all the subsequent cards.